What is the drainage fixture units for a shower?

• A. 2 DFU
• B. 3 DFU
• C. 4 DFU
• D. 5 DFU

Answer: (B)

Drainage fixture units (DFU) measure how much drainage load a fixture imposes on the sanitary system. Each fixture has a DFU value, and you add those values to determine the required pipe size and venting for a drain run.

A shower is assigned 3 DFU in this code table, which reflects its relatively high instantaneous discharge compared to smaller fixtures like a lavatory. So, when you look at a single shower, it contributes 3 DFU to the branch or group it serves. When sizing, you sum all DFU values on a drainage run and choose a pipe size and venting arrangement that can handle that total. With a single shower, the governing DFU is 3, which often corresponds to the minimum sizing for that fixture on typical installations.